Apparatus for improving sharpness when recording continuous-tone pictures

ABSTRACT

Improved sharpness is obtained in an arrangement for recording continuous-tone pictures in which electro-optic picture scanning apparatus produces picture signals which are applied to an electro-optic recorder to reproduce the picture on a recording medium. Circuits for generating a sharpness signal and for modulating the sharpness signal in dependence upon the picture content of at least a portion of the picture pattern are provided. The modulated sharpness signal is then superimposed on the picture signals to influence the sharpness of pictures recorded by the recorder.

This is a division of application Ser. No. 365,486, filed May 31, 1973,and is related to U.S. application Ser. No. 549,485, filed Feb. 12,1975, now U.S. Pat. No. 4,005,485.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and an apparatus for improvingsharpness when recording half tone pictures, and is more particularlyconcerned with such a method and apparatus wherein optical/electricalscanning of picture patterns produce picture signals which aresuperimposed with a sharpness signal that is derived during scanning forincreasing sharpness when recording.

2. Description of the Prior Art

Methods and apparatus are known in the art of reproduction techniquewhereby a single or a multi-colored half tone picture pattern isstretched as a top viewed picture, or as a translucent diapositive on ascanning drum, and is opto/electrically scanned. The scanning takesplace in such a way that a dot-shaped light beam is directed onto thepicture pattern to scan the picture pattern along the drum in aspiral-like manner by means of rotation of the drum and by means of anaxial movement of the light beam. The light which is reflected ortransmitted from the picture pattern is separated in multi-colorprinting by means of dichroic filters into the spectral regions of thebasic colors cyan, magenta and yellow, and is transformed byphotoelectric converters into electrical signals which constitute colorseparation signals. These color separation signals then control arecording member, such as an engraving needle or a recording lamp, bymeans of which the individual color separation signals are reproduced ona recording medium which is stretched on a recording drum. The movementof the recording drum, as well as the movement of the recording member,is synchronous with the scanning drum and with the scanning light beamso that the recording drum and the scanning drum rotate at the samespeed or, if enlargement or reduction is desired, the recording speed isfaster or slower than the scanning speed for reproduction. The samefacts hold true for the relative axial movement of the scanning memberwith respect to the recording member, and thus to the recording medium.

Since the colors used during the printing process, the printing colors,are incomplete, and since also other parameters occur during the entirereproduction process which influence the final color of thereproduction, the color separation signals are subjected to one orseveral electronic treatments during transmission from theoptical/electrical converter to the recording member, to neverthelessachieve the desired coloring during the printing process. Theseinfluences are generally gradation changes, color return and colorcorrection.

Since the scanned picture pattern primarily constitutes a photographicpicture which loses part of the sharpness contained in the originalpicture during development of a film, by subsequent enlargement or byoptical printing, several attempts are made to regain the lost sharpnessduring the reproduction process. In addition to the color separationsignals, a second picture signal is derived, which for an increase insharpness, is again directed to the color recording medium. This picturesignal will hereinafter be designated the sharpness signal.

Sharpness signals are provided, according to two principles. In onemethod, the picture signal which is derived during scanning of thepicture pattern is deducted from the color separation signal. To achievethis result, the color separation signal is differentiated once orseveral times and the reslt in sharpness signal is subtracted from thecolor separation signal. The resulting signal is subsequently furtherprocessed as a sharpened color separation signal.

In another method, a so-called outer field is additionally scanned inaddition to the scanning of a sharp point corresponding to the non-sharpmasking in the photograph and reproduction technique. The signal whichis achieved, and which constitutes the medium luminance of the outerfield, is subtracted from the color separation signal. The differencesignal is the sharpness signal and is added to the picture signal. Asharper signal is created which is correspondingly further processedduring printing.

The method just-mentioned offers the advantage that the lost sharpnessis regained; however, there is also the possibility that portions of thepicture which were already relatively sharp in the original arereproduced with excessive sharpness. However, if the sharpness isreduced strongly, detailed portions of the picture, such as textiles andornaments, are not reproduced with sufficient sharpness.

SUMMARY OF THE INVENTION

The present invention has as its primary object the provision of anarrangement for electro-optical reproduction of continuous tone pictureswhich do not have the aforementioned disadvantages and by means of whichimprovements in picture sharpness can be carried out separately anddifferently for individual parts of a picture.

The foregoing object is achieved according to the invention in that thesharpness signal is changed in dependence upon the picture content ofthe picture pattern before superposition of the sharpness signal withthe picture signals.

It is known to direct a sharpness signal to the picture signal with anamplitude which is constant for the entire picture. However, thismeasure covers the entire picture so that a local change of the picturesharpness is not possible. According to a preferred embodiment of theinvention, the sharpness signal is changed by a mask signal which isprovided by synchronously scanning a mask with the picture pattern andderived from the picture contents of the picture pattern.

The change of the sharpness signal can be controlled in an advantageousmanner by means of a color selection circuit which is controlled by thepicture signals and by means of signals which are derived from thecontrast of the picture pattern. In this instance, the sharpness signalis preferably diminished in the case of a large contrast of the picturepattern.

A preferred further development of the invention, which in many cases issufficient, resides in a technique for switching the sharpness signal onand off in dependence on the picture contents of the picture pattern.

An arrangement is provided for the implementation of the method of thepresent invention comprises an electro-optical scanning device forrecording the picture pattern, a device for deriving a sharpness signaland a device for superimposing the sharpness signal over the picturesignal prior to recording. According to the invention, this circuitarrangement is characterized in the provision of apparatus formodulating the sharpness signal onto the picture signal in dependence onthe picture contents of the picture pattern. This apparatus can becontrolled by means of a switching mask and/or a color selection circuitand/or a contrast evaluation circuit. The modulation apparatus canpreferably be designed as a switch.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the invention, itsorganization, construction and operation will be best understood fromthe following detailed description of a preferred embodiment of theinvention taken in conjunction with the accompanying drawings, on which:

FIG. 1 is a schematic illustration of a reproduction arrangement forrecording continuous pictures, specifically showing the derivation of asharpness signal and several possibilities for influencing the sharpnesssignal by picture contents of the picture pattern;

FIG. 2 is a schematic circuit diagram of an exemplary apparatus forrotating a scanning light point by means of an electron beam tube; and

FIG. 3 is a schematic circuit diagram of a color signal detector circuitwhich may be employed in the apparatus illustrated in FIG. 1.

FIG. 4 is a schematic circuit diagram of a multiplier which may beemployed in the color detector of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a scanning drum which has a translucent surface forcarrying translucent pictures, for example a diapositive 2. Another drum3 is provided which serves for stretching and holding of a mask 4 and arecording carrier 5. The drums 1 and 3 are driven by a motor 7 via ashaft 6.

A scanning system 9 is simultaneously driven by the motor 7 via a feedscrew 8. The scanning system 9 serves for a scanning of the diapositive2. Likewise, a scanning system 10, which serves for scanning the mask 4,and a recording system 11, which is assigned for illuminating therecording carrier 5, are driven by the motor 7 via the feed screw 8.

A light source 12 emits a scanning light beam 15 which is directed ontoa picture point 19 of the diapositive 2 by way of lens system 13 and 14through a hole 16 of a mirror 17 and a mirror 18 which is positionedwithin the interior of the scanning drum 1. The arrangement of the lightsource 12, the lenses 13 and 14, as well as the mirror 18 are arrangedin such a way that the light beam 15 is focused onto the picture point19 which is to be scanned. After passing through the diapositive 2, thelight beam 15, which is modulated with the picture content of thepicture point 19, is passed by way of a lens 20 to a color separationsystem within the scanning system 9. The light beam 15 reaches the colorseparation system by way of the lens 20 and a hole 21 in a mirror 22.The color separation system comprises dichronic filters 23 and 24 and aplurality of optical/electrical converters 25, 26 and 27. The scanninglight beam 15 is split into three sub-beams which represent the spectralregions of the basic colors, magenta, cyan and yellow, which then accrueat the outputs of the optical/electrical converters as electrical colorseparation signals which are also referred to as primary colorseparation signals.

The optical system just-described comprises an additional scanningarrangement for the outer field of the picture point 19 of thediapositive 2. This additional scanning arrangement comprises a cathodebeam tube 28 having a screen 29 on which a rotating luminous spot 30 iscreated which causes a scanning light beam 31 to be directed by way of alens 32 to the mirror 17. The mirror 17 reflects the beam 31 and directsthe same through a lens 14 to the mirror 18 which directs the beam to apicture point 33 which scans the diapositive 2. The picture point 33circles the picture point 19 in synchronism with the rotation of the dot30 created on the screen 29 of the picture tube 28. From the picturepoint 33, the light beam 31, which is modulated with the picture signalcontents of the area surrounding the picture point 19, reaches a furtheroptical/electrical converter 34 by way of the mirror 22. Theoptical/electrical converter 34 generates a corresponding electricalsignal, a so-called outer field signal. In order to completely dot-scanand linewise-scan the entire picture surface of the diapositive 2, thescanning drum 1 rotates and simultaneously the scanning system 9 travelsparallel to the axis of rotation of the drum 1 as it is driven by thespindle 8 along the drum 1. For this purpose, it is necessary that thelight source 12, the lens 13, the mirror 16, the lens 14, the mirror 18,the cathode beam tube 28 and the lens 32 by mechanically fixed to thescanning system 9 in order to be shifted axially with the scanningsystem 9 along the path defined by the spindle 8. Therefore, it isprovided that the diapositive is scanned dot wise and linewise in aspiral line due to the relative movement between rotation of the drumand the entire described scanning system.

The signals created in the optical/electrical converters 25, 26 and 27which constitute the known primary color separation signals for magenta,cyan and yellow reach the lines 35, 36 and 37. A switch 38 is providedthrough which the respective color signal to be recorded is connected tothe recording system 11. Usually, there is a color correction circuitconnected in the lines 35, 36 and 37 which, for reasons of clarity, havebeen omitted since such apparatus does not contribute to the explanationof the principles of the present invention. The recording of the signalsarriving from the switch 38 takes place by means of the recording system11 which, for example, contains an amplifier 39 controlled by way of theline 40 and which has an output signal connected to control a recordinglamp 41 to create a light beam 42 which is focused by means of an objectlens 43 onto the recording carrier 5 carried on the drum 3. Therecording carrier 5 preferably comprises light sensitive material onwhich the light beam 42 records a screw-type line due to the relativerotational and axial movement of the drum 3 and the recording system 11,whereby the recorded line accurately corresponds to the scanning of thediapositive 2.

The outer field signal is simultaneously created in anoptical/electrical converter 34 during picture scanning and recording.The outer field signal is transmitted by way of a line 44 to an RCfilter circuit consisting of a resistor 45 and a capacitor 46. Thesignal is then applied to a subtracter 48 which has another inputconnected to the line 35 by way of a decoupling resistor 47. Thesubtracter 48 is a differential amplifier which has its output connectedto the collector-emitter path of the transistor 50 and on through a signinverter 51 to the collector-emitter path of a further transistor 53from where it is extended, via a variable resistor 54, to the primarycolor separation signal on the line 40 as a sharpness signal to increasethe sharpness during reproduction. If the collector-emitter path of thetransistors 50 and 53 were replaced by conductive sections, this type ofsignal feeding to the primary separation signals would result in theknown lack of sharpness. Deviating from this known condition, in thepresent invention the transistors 50 and 53 are connected into thesignal path of the outer field signal as modulators or signal switches.In case the picture scanning point 33 circles about or scans as an outerfield to the picture point 19 a surface of various density, the signalof the optical/electrical converter 34 shows a high frequencyalternating amplitude. This signal is directed by way of a resistor 55and a capacitor 56 to an amplifier 57 which only permits the negativesignal amplitude to pass and which is connected to the base of thetransistor 50. For adjusting the working point of the transistor 50, aresistor 59 is connected between the base of the transistor and thepositive pole of an electrical supply (not illustrated). Similarstructure is provided for the transistor 53 wherein a resistor 52 isconnected between the base of the transistor and the positive pole ofthe electrical supply. The negative signal supplied from the diode 58blocks the transistor 50 whereby the sharpening signal which is receivedfrom the optical/electrical converter 34 by way of the RC circuit 45, 46at the collector of the transistor 50 is not allowed to pass thecollector-emitter path of the transistor so that the transistor isblocked. This only occurs if a signal with a high frequency alternatingamplitude is supplied by the optical/electrical converter 34, acondition indicating that the outer field about the picture point 19constitutes an area of varying density.

If the outer field has a homogeneous density, blockage of the transistor50 will not occur and the sharpness signal is permitted to traverse thecollector-emitter path of the transistor 50. The creation of the outerfield signal from which the sharpness increasing signal is derived takesplace as mentioned above by way of the rotating luminous point 30 of thecathode beam tube 28. In FIG. 2 a circuit arrangement for carrying outthe circular deflection of the electron beam is illustrated. Theelectron beam tube 28 comprises, as is well known in the art, a picturescreen 29 on which the point 30 is displayed, a pair of verticaldeflection plates 69, 70 and a pair of horizontal deflection plates 64,65. An electron beam generating system 61 is connected to the cathodestructure of the tube 28 to generate an electron beam as is well knownin the art. The control circuit 61 for producing the electron beam hasnot been illustrated in greater detail since it only contains apparatusfor providing constant voltages for adjusting the working point of thecathode beam tube 28. In addition to this structure which isschematically illustrated in FIG. 1, a control circuit 61 is alsoillustrated for controlling the deflection of the electron beam. In FIG.2 the control circuit 60 is shown in greater detail as comprising atransformer 63 which is controlled by way of a high frequency generator62. The transformer 63 includes a secondary winding which is connectedto the horizontal (X) deflection plates 64 and 65 of the cathode beamtube 28. In order to achieve a circular deflection of the type ofLissajou figures, an AC voltage which is phase shifted by 90° is derivedfrom the X-deflection voltage by tapping a voltage by way of a capacitor66 and a resistor 67 from the secondary winding of the transformer 63.This tap voltage is applied to an amplifier 68 and to the vertical (Y)deflection plates 69 and 70 of the cathode ray tube 28. The frequency ofthe high frequency generator 62 should be a multiple of the picturepoint scanning frequency so that the outer field is scanned withsufficient speed about the just-scanned picture point.

Another possibility for changing the effectiveness of the sharpnesssignals should be provided wherein the sharpness signals are switchedthrough depending on a chosen pattern color. It may be desired, forexample, to transmit skin colors during the reproduction process withoutincreasing picture sharpness. For this purpose, a color evaluationcircuit 71 is provided which functions to emit a negative signal by wayof a diode 72 if the chosen color in the picture is scanned. The diode72 is connected to the base of the transistor 53 which is blocked if thebase voltage becomes negative to prevent sharpness signals from passingto the recording system 11 by way of its collector-emitter path.

An exemplary color evaluation circuit 71 is illustrated in greaterdetail in FIG. 3. The primary color separation signals, magenta, cyanand yellow, reach the color evaluation circuit 71 on the lines 35, 36and 37. Differences between fixed values mg_(o), cy_(o) and ge_(o) areformed between the respective primary color separation signals magenta,cyan and yellow which are assigned to special characterizing colors.This occurs in that the primary color separation signals are directed ineach case to an input of an amplifier 76, 77 and 78 which are connectedas differential amplifiers. At the other inputs of the amplifiers 76, 77and 78, the fixed signal values mg_(o), cy_(o) and ge_(o) are fed by wayof respective variable resistors 79, 80 and 81 which are commonlyconnected to the positive pole of the electrical supply. The outputs ofthe amplifiers are directed to a multiplication stage 82 whichmultiplies these signals with each other. The circuit structure of themultiplier 82 is illustrated in FIG. 4. The outputs of the amplifiers76, 77 and 78 are connected with the inputs X_(in), Y_(in) and Z_(in) ofthe multiplier stage 82. The multiplier stage 82 comprises two equalmultipliers 821 and 822 which are integrated circuits. These integratedmultipliers are available from Intersil Inc., 10900 N, Tantau Ave.,Cupertino, Ca. 95014 and are described in the "Application Bulletin A011 --A Precision Four Quadrant Multiplier" by Bell ONEIL, June 1972. Anactual circuit correction of the integrated modulator (type 8013) isillustrated in FIG. 8B of the application bulletin.

The output signal of the amplifier 76 is fed to the X_(in) input(terminal b) of the multiplier 820; the output signal of the amplifier77 is fed to the input Y_(in) and to the terminal c of the amplifier viaa voltage divider consisting of the potentiometer 821 which is axiallyconnected to a ground resistor 822. The terminals a and g of themultiplicator are short circuited as shown in FIG. 9B of the applicationbulletin. The terminals d, e and f of the multiplier are connected tothe center taps of ptentiometers 823, 824 and 825 which are respectivelyconnected to supply voltages of +15 V and -15 V.

At the output g of the multiplier 820' appears the quantity (^(X) in.sup.. Y in)/10 i.e. the multiplication of the output signals of theamplifiers 76 and 77.

This signal is again multiplicated with the output signal of theamplifier 78 by way of the multiplier 820'. The output of the multiplier820 is connected to the input b' of the multiplier 820' and the outputsignal of the amplifier 78 is fed to the terminal d of the multiplier820' via the potentiometer 821' which is connected to a groundedresistor 822'. The connection of the terminals a' and g' and the wiringof the terminals d', e' and f' by the potentiometers 823', 824' and 825'is equal to the wiring of the multiplier 820. At the output terminal g'of the multiplier 820' appears a signal which is the product of theoutput signals of the amplifiers 76, 77 and 78.

If special color signals mg, cy and ge which are almost equal to theadjusted fixed signal values mg_(o), cy_(o) and ge_(o) are received bythe color evaluation circuit 71, the signal occurring at the output ofthe multiplication stage 82 is at a minimum value. This signal isinverted by the amplitude inverter 83 into a maximum negative valuesignal and is passed onto the diode 72 which then blocks the base of thetransistor 53 whereby a sharpness signal is not passed on to therecording system 11.

The effect which is therefore achieved provides that, for example, skincolors which are scanned in the picture can be recorded withoutincreased sharpness so that skin tones can be recorded in a more subduedmanner.

It is a further preferred possibility to influence the sharpness signalin accordance with the picture contents that are synchronous andregister in a stable manner with the original picture pattern. For thispurpose, a mask is scanned to provide scanning signals for influencingthe sharpness signals. More specifically, the drum 3 carries a mask 4which is scanned by means of the scanning system 10. The picture parts85 which are colored black in the mask are to be recorded under theinfluence of the sharpness signal, that is they are to be more sharplyreproduced. The sharpness signal is derived from a primary colorseparation signal supplied by the optical electrical converter 27 to theline 35. The line 35 is further connected to a pair of RC circuits whereit is twice differentiated. These RC circuits comprise a first resistor86 and a first capacitor 88 and a second resistor 87 and a secondcapacitor 89, respectively. The second RC circuit is connected to a signinverter 90 which is, in turn, connected to the collector of atransistor 91. The transistor 91 is effective as a signal modulator orsignal switch which controls transmission of the twice differentiatedcolor separation signal to the line 40 and the recording system 11 byway of a resistor 92. The base of the transistor 91 has its workingpoint adjusted by means of a resistor 98 which is connected to thepositive pole of the electrical supply. The base of the transistor 91 isalso connected to the anode of a diode 93 of the scanning system 10. Thelight beam for scanning the mask 4 is not illustrated in order to avoidconfusion in the drawing. For this purpose, however, an arrangement canbe used as was already described in connection with the light source 12,the lenses 13 and 14 and the mirror 18. This beam creation system isalso moved corresponding to the axial shifting of the scanning system 10as it is driven by the spindle 8 in the axial direction along the mask4. The light beam passes from the scanned point 96 of the mask 4 througha lens system 97 to an optical/electrical converter 94 which generatessignals in accordance with the mask pattern.

The sharpness signal can only pass the transistor 91 if the signalcreated in the scanning head 10 is small, which means that black pictureparts are scanned.

The principle along which the invention is based, namely to influencethe sharpness signals in dependence on the picture contents, is notlimited to the prior described coupling possibilities. Signals which areproduced in a different manner can also be used. For example, thepicture point 33 scanning the outer field can also be created by aneven, constant surface illumination. For example, a geometric form ofillumination may be employed and may be shaped as a ring, star orsector. In the case of the sector-shaped breakdown, the individualsectors are separated at the location of the mirror 22 and are passed onto, for example, four optical/electrical converters.

If the smallest signal created is subtracted from the largest signalcreated, a contrast increasing signal will also be provided which can bedirected by way of the signal switch or signal modulators 50, 53 or 91to the signal to be recorded by way of the line 40.

Although I have described my invention by reference to particularexemplary embodiments thereof, many changes and modifications of theinvention may become apparent to those skilled in the art withoutdeparting from the spirit and scope of the invention. I therefore intendto include within the patent warranted hereon all such changes andmodifications as may reasonably and properly be included within thescope of my contribution to the art.

I claim:
 1. An arrangement for improving sharpness in the recording of acontinuous-tone pictures, comprising: electro-optic picture scanningmeans for scanning a picture to produce picture signals; a recordingmedium; electro-optic recording means connected to said picture scanningmeans and responsive to said picture signals to produce said picture onsaid recording medium; means for generating a sharpness signal;modulating means for modulating said sharpness signal in dependence uponat least a selected portion of the picture pattern being scanned for itscharacteristics; control means for generating a control signal forinfluencing the modulation of said sharpness signal; and means forsuperimposing said modulated sharpness signal and said picture signalsto influence the sharpness of pictures recorded by said recording means.2. An arrangement according to claim 1, wherein said control meansincludes a color selection circuit connected to said picture scanningmeans, said picture scanning means further comprising means forgenerating color separation signals representing a scanned color; saidcolor selection circuit includes means for comparing said colorseparation signals with predetermined signals representing a color to beselected and means for generating said control signal for influencingthe modulation of said sharpness signal when said color is selected. 3.An arrangement according to claim 1, wherein said control means includesa contrast evaluation circuit for generating said control signal forinfluencing the modulation of said sharpness signal.
 4. An arrangementaccording to claim 1, wherein said modulating means includes a switchfor connecting and disconnecting the sharpness signal with respect tosaid recording means in response to said control signal.
 5. Anarrangement for improving sharpness in the recording of continuous-tonepictures, comprising: electro-optic picture scanning means for scanninga picture to produce picture signals; a recording medium; electro-opticrecording means connected to said picture scanning means and responsiveto said picture signals to produce said picture on said recordingmedium; means for generating a sharpness signal; modulating means formodulating said sharpness signal in dependence upon the picture contentof at least a portion of the picture pattern being scanned; controlmeans for generating a control signal for influencing the modulation ofsaid sharpness signal; and means for superimposing said modulatedsharpness signal and said picture signals to influence the sharpness ofpictures recorded by said recording means, said control means includinga picture pattern mask and means for scanning said mask to generate saidcontrol signal for influencing the modulation of said sharpness signal.